At the present time, the treatment of metastatic bone cancer (malignant tumors or lesions) is usually ineffective. Direct radiation therapy is usually ineffective. The patient undergoing radiation therapy suffers excruciating pain and eventually dies. During the disease, morphine injections are continually administered in an attempt to alleviate the pain and suffering. If the treatment involves chemotherapy, there are side effects which are very undesirable. Furthermore, chemotherapy is not often effective.
The effects of metastatic bone cancer are particularly devastating when the bone cancer appears after an ostensibly successful treatment of another form of cancer, such as breast cancer or prostate cancer. For as yet unknown reasons, hormonal cancers such as breast and prostate cancer have a tendency to metastasize to bring about bone tumors. It would certainly be desirable to increase the cure rate of breast and prostate cancers by successfully treating metastatic bone cancer.
In the diagnosis and treatment of certain cancers, radioactive tagged particles have been resorted to in the prior art. For the most part, however, this method has been limited to the treatment of cancers of the cervix or ovaries. The use of these existing radioactive tagged particles are wholly unsatisfactory for the treatment of bone cancer.
Radioactive tagged compounds, when administered to a patient, may not have a high degree of specificity for the malignant lesion. As a result, unwanted radiation is delivered to other parts of the body, thereby destroying healthy tissue. Even if the tagged compound is organ specific, it often does not have a high affinity for the lesion itself, thereby destroying healthy tissue in the organ.
Agents have been tried in the past that employ radioactive labelled agents that seek out cancerous bone tissue when administered systemically. For example, Dr. Ralph Robinson, University of Kansas Medical Center, Kansas City, Mo., has treated over 100 patients with Strontium-89 for treatment of metastatic bone cancer. His results are acceptable from the standpoint of effectiveness in treating the cancer; however, the results are not acceptable from the standpoint of safety. More specifically, the degree of malignancy is reduced and the pain is reduced; however, the dose of radioactivity to bone marrow is unacceptably high. The radioactive emissions from Strontium-89 include high energy beta emissions (e.g. 800KeV) that are sufficiently energetic penetrate through bone to bone marrow. The high levels of beta emissions account for Strontium-89 as being unacceptable from the standpoint of safety to healthy bone marrow tissues. Furthermore, Strontium-89 has a 54-day half-life which is undesirably long.
In another use of radioactive labelled agents for treating bone cancer by systemic administration, Dow Chemical Company and researchers at the University of Missouri reactor are using a bone treating agent (hydroxymethyldisphonate, HMDP) to which they attach a Samarium-153 label. Preliminary results appear promising from the standpoint of effectiveness in treating the malignancy; however, the results are indeterminate from the standpoint of safety with respect to healthy bone marrow tissue. The radioactive emissions from Samarium-153 include a large portion of high energy beta emissions (e.g. 600-700 KeV) that are sufficiently energetic to penetrate through the bone and enter the highly sensitive bone marrow where they can do considerable damage such as bringing about aplastic anemia or leukemia. The high levels of beta emissions account for Samarium-153 as being unacceptable from the standpoint of safety to healthy bone marrow tissues even though the half-life of Samarium-153 is approximately only two days.
In the case of bone cancer, we have noted that even if the radioactive tagged compound does have a high affinity for the malignant tissue, it is imperative that the radioactive tagged compound does not emit high energy particles such as high energy beta particles. These high energy particles will penetrate to the bone marrow, thereby causing radiation damage which is undesirable. Bone marrow is highly susceptible to being damaged by radiation, and it is imperative that radiation treatment of malignant bone tissue does not damage the bone marrow.